Microsoft has an important business reason as to why GitHub needs to retain its quality - they have access to a universe of confidential corporate data - source codes, inventions, product issues, workflows and so on. They can look up what companies are up to and use that to create their own competing products. Something like Amazon does when they ask sellers on the platform to reveal all their leads and suppliers and then introduce their own cheaper version of the product. Only that Microsoft does not have to ask for this, as they already have all this data. I don't think there is evidence now that Microsoft is doing anything with this data, but it only takes a change in the management.